1) Field of the Invention
The present invention relates to an optical information recording medium on which holographic recording is performed by irradiating a signal light and a reference light, a method of recording information on the optical information recording medium, and a method of manufacturing the optical information recording medium.
2) Description of the Related Art
Compared with a conventional surface recording technology such as magneto-optical recording or phase change optical recording on an optical disk, a holographic recording is gaining an attention because of its ability to implement a high-density, high-capacity, and high-speed recording. One of the holographic recording type medium is a holographic storage, which is described in, for example, H. J. Coufal: Holographic Data Storage, Springer, Berlin, p. 101-111, p 171-197, p 199-208, 2000.
The conventional recording method for the holographic storage must cope with a vibration problem in an optical system to get a stable recording of an optical interference pattern. Therefore, high precision mechanical components and positioning mechanism are required, and since the recording is based on a two-beam interference method, it is difficult to make a size of the optical system compact. Furthermore, since a recording medium to be used is required to be an optically flat disk substrate material, the recording medium lacks of the concept of address, and as a result, the recording medium is incomplete as a rewritable medium. Besides, the recording medium is incompatible with an existing optical disk.
As a new recording method intended to solve the problems described above, a polarized collinear holographic method is proposed. The method is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-123949. An optical recording medium having a reflection layer provided on its rear surface is employed, and a reference light and a signal light are coaxially incident on an optical path. In other words, input and output of an information are performed coaxially in the same direction. This makes a mechanical control required for recording easy, and since tracking servo control is exerted to read address information based on information preformatted on the optical recording medium, it is possible to make a random access to the medium.
However, if the optical recording medium conventionally used for the polarized collinear holographic recording is employed, an efficient recording cannot be ensured without an aid of a high power laser for recording. As a result, an intensity of a read light is low and a sufficiently high signal-to-noise-ratio (SNR) cannot be obtained. To make use of a performance of the recording medium, to record information using a lower power laser and obtain a high-intensity read light at a higher SNR during reading operation, a medium design considering an energy density of the signal light is required. Unfortunately, such a recording medium has not yet been achieved.